1. Field of the Invention
The present invention relates to a display device capable of displaying an image recorded, for example, on a developed film.
2. Description of Related Art
Known display devices such as film viewers have been arranged in general to convert a negative image into an electrical signal by using a CCD (charge-coupled device) camera and, after that, to display an image carried by the electrical signal on a CRT (cathode ray tube) display or on a liquid crystal display. Some of the known display devices are arranged to optically project on a screen a positive image recorded on a positive film. The known display devices also include various electronic image display devices arranged to display motion pictures on a CRT display or on a liquid crystal display, for example, by changing still images from one over to another at a television rate.
Meanwhile, spatial light modulators (SLMs) have been developed for display devices which are capable of inputting, storing, reading and erasing two-dimensional signals. The spatial light modulators are either of a photo-address type arranged to have a light image signal as an input or an electric-address type arranged to have time-serial electric signals as an input. The photo-address type spatial light modulators include a liquid crystal spatial light modulator, which is composed of a liquid crystal layer arranged to modulate a light signal and a light transmission layer arranged to transmit writing light energy to the liquid crystal layer. In a case where the photo-address type spatial light modulator is used for a liquid crystal projector, for example, a light image is displayed on a small-sized CRT display. The liquid crystal spatial light modulator having the light transmission layer and the liquid crystal layer arranged one after another is provided over the whole surface of the small-sized CRT display. The light image of the CRT display is radiated to the surface of a photoconductor, such as a CdS (cadmium sulfide) member. The impedance of the photoconductor drops at its part illuminated with the light to cause a higher voltage to be applied thereto than other parts not illuminated with the light. As a result, voltages are applied to the liquid crystal according to a distribution of intensity of the input light image. The transmissive light quantity of the liquid crystal is thus caused to vary by a hybrid field effect thereof. The image obtained on the small-sized CRT display is displayed on a screen, with the quantity of light transmitted through the liquid crystal projected on the screen in an enlarged state. The light transmission layer of the liquid crystal spatial light modulator is selected from among photoconductive materials such as CdS, ZnSe, a-Si (amorphous silicon), etc., photo-refractive crystals such as BSO (bismuth silicon oxide), BGO (bismuth germanium oxide), TBO, etc., and compound semiconductors of the III-V group or the II-VI group. The light transmission layer must have a high degree of detection sensitivity, a high resolution and a quick response. For the converting function of the liquid crystal layer which is required to have a quick response and a high contrast-giving power, a material for the layer is selected from among a group of materials including a twisted nematic liquid crystal, an electro-optic crystal such as LiNbO.sub.3 (lithium niobate), BSO, etc., or an organic non-optical crystal, etc. Spatial light modulators of high performance thus have been developed.
However, in the above-stated display device using a CCD camera, the density of picture elements of the CCD which is an image pickup device and that of a display are coarse. For example, the face of a person on display is hardly discernible. The display device of such a kind is thus not suited for displaying silver-halide photographs.
As for the display device using a positive film, the positive film itself has narrow latitude (exposure tolerance) for photographing and is not popularly used by people as it necessitates taking heed to photo-taking conditions. The positive films also necessitate a greater amount of time and labor than negative films in developing them and in printing some of frames after they are developed.
In a case where a negative film is used, it is necessary to take into consideration the question of quantity of light. A rate of light transmissible through developed negative films carrying images of ordinary scenes is less than 10% on the average. Projection of the image in an enlarged state needs an excessively large quantity of light and thus requires use of a large device. Therefore, it is difficult to prepare a compact and handy film viewer for negative films.
Further, all the display devices mentioned above are arranged mainly for showing moving images. Therefore, the number of picture elements used for them is extremely insufficient, in terms of resolution, for showing still images. There has been no electronic display device arranged to be capable of showing images with such a high quality that is well compared to the quality of a silver-halide print. A display device developed for a high-definition TV is close to such an electronic display device. Although the display device of that kind shows some improvement over a normal TV system in respect to the number of picture elements, its driving rate either still remains unchanged from an ordinary TV rate or at about 60 Hz which is only twice as much as the ordinary TV rate. Therefore, when a somewhat bright still image is displayed, the image on display shows some flickers to the human eye and is not adequately viewable.